The findings of this multi-site study emphasise the importance of Organisational Culture for integrating clinical information systems into intensive care units. A novel model, the Iterative Systems Integration Model, has two principle components, these being Organisational Culture and the Actual Usefulness of the clinical information system. The model is derived from empirical data collected in four intensive care sites in England and Denmark, with one site being used to validate the model. The model highlights clinical information systems as directly affecting the work processes of the sites investigated, which in turn affect the Organisational Culture and Actual Usefulness of the clinical information system used, and these features affect clinical information system integration. This forms an iterative process of change as clinical information systems are introduced and integrated. Intensive care units are complex organisations, with complex needs and work processes. The impact of clinical information systems on these work processes is investigated in this thesis using Role Activity Diagrams. These diagrams are analysed to show that although clinical work processes are consistent at each site, the information processes differ. Intensive care information processes are found to have the potential to be much simplified with the introduction of seamless clinical information systems. Qualitative data collectio n methods were deployed, i. e., observations, interviews, and shadowing of clinical staff, together with a questionnaire at each site for further validation. Data were analysed using grounded theory to extract salient variables, which informed the development of the model. These factors were indicative of the Organisational Culture of the sites investigated and the Actual Useftilness of the clinical information systems being used. It was posited that clinical information systems that reconcile expectations of both hospital management and clinical staff - and that have the potential to adapt to their organisational environment - have a greater chance of surviving in complex environments such as intensive care. Despite decades of Health Infon-flatics, no such systems exist in their entirety; this research shows that 'ancient problems' of clinical information systems integration are still prevalent, and presents the Iterative Systems Integration Model, the application of which may assist with the integration of clinical information systems in intensive care.